Nine persons - I, J, K, L, M, N, O, P and Q joined an organization in different months starting from January to September of the same year, but not necessarily in the same order.
N joined in a month having even number of days. Neither M nor N joined in February.
| | | Case 1 | Case 2 | Case 3 |
| Months | Days | Persons | Persons | Persons |
| January | 31 | | | |
| February | 28/29 | | | |
| March | 31 | | | |
| April | 30 | N | | |
| May | 31 | | | |
| June | 30 | | N | |
| July | 31 | | | |
| August | 31 | | | |
| September | 30 | | | N |
Three persons joined between N and M, who joined immediate after I.
Neither M nor N joined in February. Thus, case 2 is invalid.
| | | Case 1 | Case 3 |
| Months | Days | Persons | Persons |
| January | 31 | | |
| February | 28/29 | | |
| March | 31 | | |
| April | 30 | N | I |
| May | 31 | | M |
| June | 30 | | |
| July | 31 | I | |
| August | 31 | M | |
| September | 30 | | N |
Two persons joined between J and Q. Neither J nor K joined immediate before I. Thus, case 3 is invalid.
| | | Case 1 |
| Months | Days | Persons |
| January | 31 | |
| February | 28/29 | J/Q |
| March | 31 | |
| April | 30 | N |
| May | 31 | J/Q |
| June | 30 | |
| July | 31 | I |
| August | 31 | M |
| September | 30 | |
L joined in June but before O.
| | | Case 1 |
| Months | Days | Persons |
| January | 31 | |
| February | 28/29 | J/Q |
| March | 31 | |
| April | 30 | N |
| May | 31 | J/Q |
| June | 30 | L |
| July | 31 | I |
| August | 31 | M |
| September | 30 | O |
Q joined before K.
Therefore, the final arrangement is:
| January | 31 | P |
| February | 28/29 | Q |
| March | 31 | K |
| April | 30 | N |
| May | 31 | J |
| June | 30 | L |
| July | 31 | I |
| August | 31 | M |
| September | 30 | O |
Four persons joined an organization between I and Q.
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